CCL:G: End of a frequency job



 Sent to CCL by: errol lewars [elewars-#-trentu.ca]
 2008 August 25
 
The general view is that it is simply wrong to use one method/basis for the optimization and another for the frequencies: consult some standard books on computational chemistry.
 E. Lewars
 ===
 Close, David M. CLOSED^mail.etsu.edu wrote:
 
 Sent to CCL by: "Close, David M." [CLOSED__mail.etsu.edu]
 Yes, that is exactly right.  As a check you could try a frequency calc.
 using the same basis set.  Usually 3 out of 4 of the "yes" are ok.
 For
 some reason the third "yes" is sometimes a "no".  I don't
 know why.
 Now a more basic question.  If you are taking a course on doing
 calculations, you are always told you must use the same basis sets in
 frequency calculations as on the original optimizations.  But people
 seem to be getting away from this are very large calculations.  If it
 takes a week to do an optimization, it might take 3-4 weeks to do a
 frequency calculation.  So people are now using smaller basis sets to do
 faster frequency calcs.  I do not happen to know if this leads to
 problems.  I do know that Berny Schlegel warned about this some time
 ago, but I do not know the current thinking on this.
 -----Original Message-----
 
From: owner-chemistry ~~ ccl.net [mailto:owner-chemistry ~~ ccl.net]
 Sent: Monday, August 25, 2008 11:29 AM
 To: Close, David M.
 Subject: CCL:G: End of a frequency job
 Sent to CCL by: Orlin Blajiev [Orlin.Blajiev,vub.ac.be]
 David, Alcides,
 Thanks for the info. I guess  G03 reports the geometry as  non-converged
 because I use different  BS in Opt and  Freq.
 Best regards,
 Orlin
 Alcides Simao alsimao[#]gmail.com wrote:
 
 Orlin:
 
This is a routine check from GAUSSIAN, made after *all* frequency jobs. You can safely discart it. Gaussian will always do that, even if
 
 you don't flag the 'OPT' option.
 Best,
 Alcides